Typical turbine casings generally are formed with a number of sections that are connected to each other. The sections may be connected by bolted flanges in any orientation and in similar arrangements. During a transient startup of a gas turbine, the horizontal joints may remain colder than the rest of the casing due to the additional amount of material required to accommodate the bolt. This thermal difference may cause the casing to be “out of roundness” due to the fact that the time to heat up the horizontal joints may be slower than that of the surrounding casing. This condition is also called ovalization or “pucker”. On shutdown, an opposite condition may occur where the horizontal joints remain hot while the casing around them cool off so as to cause the opposite casing movement or ovalization. Similar issues may arise with the use of one or more false flanges on the casing.
There is therefore a desire to reduce or eliminate the presence of thermal gradients that may cause an “out of roundness” about the joints or elsewhere about a casing for a rotary machine such as a turbine. Elimination of these thermal gradients should promote a longer lifetime for the equipment with increased operating efficiency due to the maintenance of uniform clearances therein.